Abstract
We present a detailed analysis of the inner mass structure of the Cosmic Horseshoe (J1148+1930) strong gravitational lens system observed with theHubbleSpace Telescope (HST) Wide Field Camera 3 (WFC3). In addition to the spectacular Einstein ring, this systems shows a radial arc. We obtained the redshift of the radial arc counterimagezs, r = 1.961 ± 0.001 from Gemini observations. To disentangle the dark and luminous matter, we considered three different profiles for the dark matter (DM) distribution: a power law profile, the Navarro, Frenk, and White (NFW) profile, and a generalized version of the NFW profile. For the luminous matter distribution, we based the model on the observed light distribution that is fitted with three components: a point mass for the central light component resembling an active galactic nucleus, and the remaining two extended light components scaled by a constant mass-to-light ratio (M/L). To constrain the model further, we included published velocity dispersion measurements of the lens galaxy and performed a self-consistent lensing and axisymmetric Jeans dynamical modeling. Our model fits well to the observations including the radial arc, independent of the DM profile. Depending on the DM profile, we get a DM fraction between 60% and 70%. With our composite mass model we find that the radial arc helps to constrain the inner DM distribution of the Cosmic Horseshoe independently of the DM profile.
Highlights
In the standard cold dark matter (CDM) model, the structure of dark matter (DM) halos is well understood through large numerical simulations based only on gravity (e.g., Dubinski & Carlberg1991; Navarro et al 1996a,b; Ghigna et al 2000; Diemand et al.2005; Graham et al 2006a; Gao et al 2012)
We present a detailed analysis of the inner mass structure of the Cosmic Horseshoe (J1148+1930) strong gravitational lens system observed with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3)
Summary and conclusions While in the standard CDM model the structure of DM is well understood through large numerical DM only simulations (e.g., Dubinski & Carlberg 1991; Navarro et al 1996a,b), we have to include the baryonic component to reach more complex, but realistic models
Summary
In the standard cold dark matter (CDM) model, the structure of dark matter (DM) halos is well understood through large numerical simulations based only on gravity Power law model for total mass distribution we consider a simple power law model for the total lens mass distribution, which has been shown by previous studies to describe well the observed tangential arc (e.g., Chae et al 1998; Keeton 2001; Belokurov et al 2007; Dye et al 2008; Quider et al 2009; Bellagamba et al 2017) This allows us to compare our model, which includes the radial arc, with previous models. Npt is the number of data points, θpjred the predicted, and θojbs the observed image position, where σ j is the corresponding uncertainty of point j This model contains six sets of multiple images in addition to the radial arc and its counterimage Since we do not have other information to infer the DM component, we fit to the data using different types of mass profiles (Sect. 4.2.2)
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